724 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS is reasonable to suppose that, on some occasions, the contaminants provide a source of foreign protein evoking an allergic contact dermatitis reaction or that high levels of a microbial metabolite will cause a primary irritant reaction. The eye, of course, is particularly susceptible to infection from contaminated cosmetics and it is also at risk from the direct effect of irritant metabolites left in a product even after the organisms producing them have been eradicated. Change of activity An interesting aspect, but perhaps not one of great significance, is the inactivation of biologically active molecules by organisms contaminating a. formulation. Several examples have now been demonstrated in the labor- atory and in some cases have been observed to occur in practice. A classic example is the destruction of penicillins by penicillinases, enzymes pro- duced by a broad range of micro-organisms. Microbial enzymes which in- activate chloramphenicol are also known (5) and the destruction of pre- servatives and disinfectants is established (6). Pharmacologically active substances can also be degraded. For instance Kedzia, Lewon and Wis- niewski (7) found that a loss of atropine of up to 20•o in eye drops could be caused by Corynebacterium and oeseudomonas spp. isolated from the eye drops and atropine itself. Recently, Grant, de Szors and Wilson (8) have shown that in the laboratory, a strain of Acinetobacter lwoffi, obtained from distilled water, utilized aspirin as a sole carbon source in a mineral salt solution. The same organism metabolized other active esters for instance it could degrade heroin to morphine. Another organism, Corynebacterium hoffnaii, which was isolated from laboratory dust, metabolized the anal- gesics aspirin, phenacetin and paracetamol. Loss of useful activity is not restricted to pharmaceutical products. For instance emphasis on the need for detergents which are biodegradable has had some repercussion and shampoos have been known to lose their surface-active properties due to degradation of the surfactants by con- taminating bacteria. Visible effects Visible growth When micro-organisms can actually be observed in or on a product then there is obviously no doubt that microbial spoilage has occurred. In fact, this is probably the most common way in which it is manifest. In liquid

MICROBIOLOGICAL SPOILAGE IN PHARMACEUTICALS AND COSMETICS 725 formulations contaminants may be seen as a sediment, turbidity or a pellicle while on more solid preparations colonies, often coloured, of bacteria, yeasts or moulds may form. Colour changes Sometimes visible spoilage is more striking, particularly if a colour change is involved. Colour changes due to alterations in the components of a product may result from pH, redox or other changes caused by the metabolic activities of an organism, or to pigment production by the con- taminants themselves. Members of the Pseudomonas genus are often implicated in spoilage of this type. These organisms metabolize a very broad range of compounds, and can also produce soluble pigments ranging in colour from blue-green to brown. In addition, they can render conditions suitable for less adaptable spoilage organisms for example they can create conditions favouring the growth of anaerobes. Similarly, in an acidic product, oxidative yeasts can cause a rise in pH by utilizing organic acids and this will encourage bacterial growth. Gas production If microbial metabolism produces gas in a sufficient amount to exceed its solubility in a product, visible bubbles, frothing and other manifestations of an increase in pressure occur. Products containing carbohydrates or other fermentable substrates are particularly susceptible to this type of spoilage. Of the latter, glycerol, an essential ingredient in many cosmetic preparations, is fermented particularly readily by some common waterborne organisms. Other changes Microbial metabolism can result in the composition of a homogeneous product becoming visibly heterogeneous. Emulsions, for instance, are notoriously susceptible to changes in physicochemical conditions hydro- lysis of the oil phase or changes in the pH of the aqueous phase will upset the equilibrium and thus cause visible changes. In liquid products changes of viscosity can be seen to occur when contaminants have broken down large molecules, utilized sugars or caused the aggregation of particles in suspension. Olfactory effects It has long been known that many micro-organisms produce character- istic odours and as early as 1923 a variety of aroma-producing bacteria had been listed (9). These aromas include the highly characteristic ones of sulphur-containing metabolites such as hydrogen sulphide, the sickly